Air circulation systems have become integral components in a wide variety of building applications, both residential and commercial. Typically, air circulation systems comprise a duct system in combination with a fan or blower and enable the selective, and oftentimes constant, recirculation of air. The circulation, or recirculation, of air may be utilized to promote a specific pressure regimen within the building, such as to provide a positive building pressure, or may instead be utilized to assist in the removal of harmful air-borne contaminants or to provide heating or air conditioning to the building as a whole. Of course, air circulation systems may be designed to accomplish one or more of these objectives.
Heating components are typically utilized in conjunction with air circulation systems to provide an influx of heat to the recirculated air, upon demand, or as a function of the operation parameters of the overall air circulation system.
Although many different types of heating components are known, direct fired heating units are oftentimes utilized to provide the necessary infusion of heat to an air circulation system. Direct fired heating units typically utilize burners, or the like, oriented in series with the duct system and act to directly heat a circulated air mass as it passes through the burner, the heated air mass being subsequently delivered to selected portions of the building. Typically, these direct fired heating units are fueled by natural gas or propane. These systems, however, are somewhat problematic as the fuel utilized by a given burner apparatus also inherently passes the by-products of combustion into the air mass itself during the heating process, thus leading to contamination concerns.
Several known air circulation systems have been designed to address the contamination concerns inherent in the utilization of direct fired burners. One type of known air circulation system utilizes damper positioning sensing to determine the percentage of recirculated air in the total air mass (known as the ‘ventilation rate’), whereby the burner is controlled, in part, on the basis of the determined ventilation rate and the permissible equivalent temperature rise of the air mass before and after it has been treated by the burner. These damper positioning sensing (‘DPS’) systems typically utilize sensors to determine the physical position of louvers in the damper units which regulate the influx of outside air, as well as for determining the physical position of louvers in those damper units which regulate the influx of recirculated air. By sensing the physical position of louvers in each of the damper units, DPS systems can estimate how ‘open’ each damper unit is and thereby calculate the likely ventilation rate for the system as a whole. DPS systems do not, therefore, directly measure the air mass travelling through any of the damper units, rather these systems rely upon an indirect method for determining the air mass flow through each of the damper units in order to calculate the ventilation rate and subsequent control of the burner element.
As will be appreciated, the accuracy of DPS systems is intimately dependent upon the accuracy of the sensors in determining the actual, physical position of the louvers in the damper units. Should there exist problems with the structural integrity of the mechanical linkages in the damper units, or if there are any other environmental or structural complications, the sensors will misreport the actual position of the louvers, and hence, determination of the air mass moving through each of the damper units will be erroneously calculated. Moreover, the presence of dirty or blocked filters within a DPS system may also cause a miscalculation of the moving air mass, a miscalculation which DPS systems are unable to detect or compensate for.
It will therefore be readily apparent that determining the ventilation rate from the indirect sensing of an air mass moving through a damper unit, as in known DPS systems, is susceptible to a myriad of structural and environmental factors which detrimentally affect the accuracy of the system as a whole. In addition, the inaccuracy of DPS systems only tend to increase in magnitude the longer the systems are in use.
Other known systems, such as CO2-based systems, exist to address the contamination concerns of direct-fired systems, however these systems also suffer from operational shortcomings due to the detrimental effect that altitude and humidity, amongst other environmental concerns, have on the accuracy of the system. Moreover, CO2-based systems have inherently limited measurement ranges which typically require large amounts of outside air to be heated, thus raising operating and maintenance costs.
With the forgoing problems and concerns in mind, it is the general object of the present invention to provide an air circulation system which overcomes the above-described drawbacks and which ensures that air flow measurements are accurately and directly monitored in light of the temperature rise in the supply air stream, thereby systematically controlling the harmful build-up of combustion by-products in the circulating air mass.